Here is some info I pulled on the Active Noise Cancellation:

"Speaking of sound, one of the more remarkable innovations to come along in years is active noise cancellation. Currently available in the Acura RL and the Honda Accord hybrid, active noise cancellation places cockpit noise-detecting microphones around the cabin, where they pick up engine or road noise. The system’s speakers then emit an opposite signal that cancels out those noises so the human ear can’t detect them, Kahn said.
Active noise cancellation is used in the Acura RL to enhance the vehicle’s quiet ride.

“In the Accord hybrid, certain functions of the hybrid system create a harmonic inside the car, so they use the system to cancel out that noise,” Kahn said. “The side benefit is a very quiet ride.”

I have noticed the "microphone" on the interior roof of the car near the rear view mirrors. I don't think replacing the speakers would affect this based on what I've read. I guess we will see....